Method and apparatus for bending sheet glass

ABSTRACT

In a bending apparatus for glass sheets, at least some of distances between conveyor rolls are set so as to be unequal, forming glass sheets having good quality and free from optical distortion. For the purpose, the distances between conveyor rolls which are provided from an outlet of a heating furnace are set so as to be unequal and to gradually expand toward a downstream direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a bending method and a bendingapparatus for glass sheets. In particular, the present invention relatesto a bending method and a bending apparatus for glass sheets whereinglass sheets heated to a bending temperature by a heating furnace areconveyed and the glass sheets are bent in a shape along a conveyer pathunder their own weight.

2. Discussion of the Background

As an apparatus for bending glass sheets during conveyance by rolls,there have been known roll-formed conveyor apparatuses (for instance,U.S. Pat. No. 4,311,509). Such roll-formed conveyor apparatuses includea plurality of conveyer rolls which are bent so as to have arbitrarycurvatures. The conveyor rolls are provided at equal distances. Theconveyor rolls provide a conveyor path having arbitrary curvatures inthe apparatuses. The glass sheets which have been heated to a softeningtemperature in a heating furnace are conveyed on the conveyor path froman outlet of the heating furnace toward a certain direction. The glasssheets which are conveyed on the conveyor path are bent in a shape alongthe conveyor path under their own weight during conveyance.

However, the conventional conveyor rolls cause striped defects on asurface of the glass sheets after forming. The striped defects areoptical distortion caused during bending the glass sheets, and thedistortion degrades the quality of the glass sheets.

The causes of the optical distortion will be explained, referred to FIG.7. FIG. 7 is a transitional view showing how a glass sheet 1 which hasbeen delivered from an outlet of a heating furnace is conveyed by aplurality of conveyer rolls 2A, 2B, 2C, 2D forming a conveyor path. Theglass sheet 1 is bent in a certain shape, being conveyed by the conveyorrolls 2A, 2B, 2C, 2D.

As shown in FIG. 7(B), when the glass sheet 1 has a leading portion 1Acontacted with the conveyor roll 2A, the leading portion 1A has heatremoved to the conveyor roll 2A. Such removal of heat causes a conveyorroll side of the glass sheet 1 to be thermally shrunk, making theleading portion 1A sag downwardly (C). As shown in (D), the saggedleading portion 1A runs onto the conveyor roll 2B when passing on theconveyor roll 2B. This creates a state that the entire glass sheet 1 isslightly lifted. As shown in (E), when the leading portion 1(A) haspassed the conveyor roll 2B, the entire glass sheet 1 returns to aposition before being lifted, and contacts with the conveyor rolls 2A,2B. (F) and (G) are viewes showing a repeat of the operations in (D) and(E). As explained, the glass sheet 1 is conveyed on the conveyor rolls1A, 2B, 2C, 2D . . . , being slightly vibrated in a vertical directionbecause of the presence of such sagging motion of the leading portion1A.

In (C)-(G), attention is directed to arbitrary points a and b on theglass sheet 1 (actually, lines perpendicular to a conveyance direction).The point a rises (D) after contacting with the conveyor roll 2A, andcontacts with the conveyor roll 2B after lowering of the glass sheet 1(E). Next, the point a rises (F) and contacts with the conveyor roll 2Cwhen having lowered (G). In other words, the glass sheet 1 sequentiallycontacts with the conveyor rolls 2A, 2B, 2C, 2D . . . , duringconveyance.

On the other hand, the point b is located above the conveyor roll 2A asshown in (D) when the glass sheet 1 is lifted. After that, the point bis located between the conveyor roll 2A and the conveyor roll 2B in (E)wherein the glass sheet 1 has lowered. This motion prevents contact withthe conveyor roll 2A. Repeats of such motion prevent contact with theconveyor rolls 2B, 2C, 2D as well. In other words, the point b does notcontact with the conveyor roll 1A, 2B, 2C, 2D . . . at all duringconveyance of the glass sheet 1.

When the conventional conveyor rolls are used, portions (e.g. the pointa) which are cooled by contact with the conveyor rolls and portions(e.g. the point b) which are not cooled by the conveyor rolls not at allcoexist on formed glass sheets. This creates differences among theseportions in terms of thermal shrinkage, and the differences areexhibited as striped defects in the formed glass sheets. This is thecauses of the optical distortion.

SUMMARY OF THE INVENTION

The present invention has been conceived, considering these problems,and it is an object of the present invention to provide a bending methodand an bending apparatus for glass sheets capable of forming glasssheets having good quality and free from any optical distortion.

In order to attain the object, the present invention provides a methodfor bending glass sheets wherein glass sheets are conveyed in a heatingfurnace to be heated to a certain bending temperature, the heated glasssheets are conveyed on a conveyor path including a plurality of conveyorrolls provided from an outlet of the heating furnace toward a downstreamdirection and having certain curvatures given thereto by the rolls, andthe glass sheets are bent in a shape along the conveyor path under theirown weight, characterized in that the conveyor rolls are provided to setat least some of distances between adjoining conveyor rolls so as to bedifferent from the other distances, and that the glass sheets areconveyed on the conveyor path.

The present invention also provides an apparatus for bending glasssheets which comprises a heating furnace to heat glass sheets to abending temperature, a conveyor for conveying the glass sheets in theheating furnace, and a conveyor path including a plurality of conveyorrolls provided from an outlet of the heating furnace toward a downstreamdirection and having certain curvatures given by the rolls, wherein theheated glass sheets are conveyed on the conveyor path to be bent in adesired shape; characterized in that the conveyor rolls are provided toset at least some of distances between adjoining conveyor rolls so as tobe different from the other distances.

As explained, the present invention is based on finding that the routcause of the optical distortion stated earlier is the equality in thedistances between the conveyor rolls, and the present invention setssome of the distances between the conveyor roll so as to be unequal inorder to improve the optical distortion. When the distances between theconveyor rolls are equal, portions which are cooled by contact with theconveyor rolls and portions which are not cooled by the conveyor rollsat all coexist in formed glass sheets. This phenomenon causes opticaldistortion in the glass sheets. On the other hand, when at least some ofthe distances between the conveyor rolls are set to be unequal inaccordance with the present invention, glass sheets can contact with theconveyor rolls at any portions thereof. This prevents striped defectsfrom being caused in the glass sheets, improving the quality of theglass sheets.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the bending apparatus for glasssheets according to an embodiment of the present invention, and thebending method for glass sheets according to an embodiment using thebending apparatus;

FIG. 2 is a front view showing an example of the arrangement of aconveyor roll in FIG. 1;

FIG. 3 is a partially enlarged sectional view showing an example of aconveyor roll in FIG. 2;

FIG. 4 is a partially enlarged sectional view showing another example ofa conveyor roll in FIG. 2;

FIG. 5 is a schematic view to explain distances between the conveyorrolls in FIG. 1;

FIG. 6 is a transitional view wherein a glass sheet is conveyed by theconveyor rolls in FIG. 1; and

FIG. 7 is a transitional view wherein a glass sheets is conveyed byconventional conveyor rolls.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the bending apparatus for glass sheets according to a preferredembodiment of the present invention will be described in detail,referring to the accompanying drawings. In FIG. 1 is shown a perspectiveview of the bending apparatus for glass sheets according to thepreferred embodiment of the present invention, and an embodiment of thebending method for glass sheets using the bending apparatus.

As shown in this figure, the bending apparatus for glass sheets 10includes a plurality of conveyor rolls 12, 12 . . . . The conveyor rolls12, 12 . . . are provided in parallel with one another to provide aconveyor path 14 defining a forming section. The conveyor path 14 formedby the conveyor rolls 12, 12 . . . is provided at an outlet of a heatingfurnace 16. In the heating furnace, glass sheets are conveyed by anadequate conveyor. As this conveyor, there are various type of measures.Since the conveyor rolls are provided from the outlet of the heatingfurnace toward a downstream direction, it is preferable that theconveyor in the heating furnace comprises a plurality of rolls.

The conveyor rolls 12 on an upstream side of the conveyor path 14 areformed in a linear shape, and the conveyor rolls on an downstream sideof the conveyor path 14 are bent so as to have certain curvatures. Thecurvatures of the conveyor rolls 12 are determined so that thecurvatures increase (radiuses of curvatures decrease) gradually from theupstream side toward the downstream side of the conveyer path 14 andchat a certain curvature is established on the downstream side of theconveyor path 14.

A glass sheet 18 is heated to a bending temperature (normally 650°C.-700° C.) in the heating furnace and is delivered onto the conveyorpath 14. The heated glass sheet 18 is bent in a shape along the conveyorpath 14 under its own weight while the glass sheet is conveyed on theconveyor path 14. The certain curvatures of the conveyor rolls aredetermined so as to correspond to a desired shape for glass sheets. Inparticular, glass sheets can have formed shape thereof slightly deformedby being cooled after bending. The certain curvatures of the conveyorrolls include curvatures that are determined, taking such deformation inthe formed shape into account.

As shown in FIG. 2, each conveyor roll 12 comprises a guide shaft 20 anda plurality of ring rolls 22, 22 . . . carried on the guide shaft 20,and is mounted to a supporting frame 38. A lefthand sprocket housing 30is provided at a left lateral end of the ring rolls 22, and a righthandsprocket housing 32 is provided at a right lateral end of the ringrolls. The supporting frame 38 has both ends provided with mountingmembers 38 a, and both ends of the guide shaft 20 are fixed to themounting members 38 a, 38 a.

At a left end of the lefthand sprocket housing 30 are provided first andsecond sprocket 30A, 30B. The second sprocket 30B is coupled to asprocket 44 of a driving motor 42 through a chain 40 so as to receive arotational force. The driving motor 42 is fixed to the supporting frame38 through bolts 46, 46 . . . . A bushing 48 is fitted in between thelefthand sprocket housing 30 and the guide shaft 20. The guide shaft 20has a stop ring 50 fitted in a portion thereof on a left end side of thelefthand sprocket housing 30, and the stop ring 50 is fixed to the guideshaft 20 through a bolt 52.

Like the lefthand sprocket housing 30, the righthand sprocket housing 32is fixed to an right end portion of the guide shaft 20. The righthandsprocket housing 32 is provided with first and second sprockets 32A, 32Blike the lefthand sprocket housing 30. Explanation of the first andsecond sprockets 32A, 32B will be omitted since these sprockets are thesame as the first and second sprockets 30A, 30B of the lefthand sprockethousing 30. The guide shaft 20 also has a stop ring 50 fitted in aportion thereof on a right end side of the righthand sprocket housing32, and the stop ring 50 is fixed to the guide shaft 20 through a bolt52. By such arrangement, both ends of the guide shaft 20 are fixed bythe stop rings 50, and the ring rolls 22, 22 are held with upper endsthereof contacted one another between the lefthand sprocket housing 30and the righthand sprocket housing 32.

The driving motor 42 is not required to be provided at every conveyorroll. When the sprockets (30A, 32A) of adjoining conveyor rolls arecoupled, the rotational motion of a conveyor roll with the drive motor42 provided can be transmitted to its adjoining conveyor roll. Therotational motion by the driving motor can be transmitted to a conveyorroll next to the adjoining conveyor roll.

The structure of the conveyor rolls will be described in detail, usingFIG. 3. In each of the conveyor rolls 12, the ring rolls 22, 22 . . .are rotatably supported on the guide shaft 20. The ring rolls 22comprise a roll body 22A and a collar 22B. The roll body 22A is formedin a cylindrical shape and has a central portion formed with a greatdiameter of through hole 22 a opening at one end surface thereof and asmall diameter of through hole 22 b opening at the other end surface.The small diameter of through hole 22 b has a hole diameter greater thanthe outer diameter of the guide shaft 20. The greater diameter ofthrough hole 22 a has a bushing 24 fitted thereinto, and the bushing 24is fitted on the guide shaft 20. By such arrangement, the ring rolls 22are carried on the guide shaft 20 so as to be rotatable.

Each roll body 22A has both end surfaces formed with annular ribs 22 c,22 c, and screwed holes 22 d, 22 d are formed at two locations of anouter peripheral surface of each of the ribs. Each collar 22B is fittedonto an outer periphery of each roll body 22A by shrinkage fit forinstance. Each collar 22B has substantially the same width as the entirewidth of each of roll body 22A, and each collar has holes 22 e formedtherein in alignment with the screwed holes 22 d in a related roll body22A.

Adjoining ring rolls 22, 22 are coupled together by a flexiblecylindrical member 26 which is provided on the annular ribs 22 c, 22 cof the adjoining ring rolls and is made of rubber. Each flexiblecylindrical member 26 has both ends formed with screw through holes 26a. Screws 28 (replaceable by tighting members such as machine screws andclips) are inserted into the screw through holes 26 a to be engaged withthe screwed holes 22 b in the related ribs 22 c, coupling the adjoiningring rolls 22, 22 together. Each flexible cylindrical member 26 has anoutwardly projecting portion 26 b formed therein throughout the entirecircumference at a central portion in a width direction thereof.

Each sprocket housing 30 and its adjoining ring roll 22 are coupledthrough a flexible cylindrical member 26 by such arrangement, the torquetransmitted to each sprocket 30B can be transmitted to adjoining ringrolls 22, 22 . . . one by one through the flexible cylindrical members26, providing each conveyor roll 20 with a rotational force required forconveying glass sheets.

In FIG. 4 is shown another example of the structure of the conveyorrolls. In this example, adjoining ring rolls 22 are coupled by a rigidcylindrical member 58 which is interposed therebetween and is formed ina bellows shape. The rigid cylindrical member 58 in a bellows shape ismade of a material having high toughness such as spring steel, and hasan expanding and contracting portion 58 a formed in an intermediateportion thereof in a width direction thereof. Both ends of the rigidcylindrical member 58 are mounted to the annular ribs 22 c, 22 c of theadjoining ring rolls 22, 22, and both ends of the rigid cylindricalmember 58 are fixed to the annular ribs 22 c, 22 c by screws 28.Coupling the lefthand sprocket housing 30 with its adjoining ring roll22 and coupling the righthand sprocket housing 32 with its adjoiningring roll 22 are made by similar rigid cylindrical members 58, and thecoupling is established by screws 28, 36 as in the first example of theconveyor rolls.

In the second example, variations in the distance between adjoining ringrolls 22, 22 caused by the vibration of the adjoining ring rolls 22, 22can be absorbed by the expanding and contracting portion 58 a in abellows shape of the rigid cylindrical member 58.

When one of the ring rolls 22 in a conveyor roll 12 is replaced by a newone in this example, a screw driver is inserted from the holes 22 e inthe relevant collar 22B, the screws 28 in the ring roll 22 to bereplaced are loosed by the driver to remove the relevant flexiblecylindrical members 26 b from the annular ribs 22 c of the ring roll,the ring roll is replaced by the new ring roll 22, and the flexiblecylindrical members 26 b are tightened to the new ring roll 22 by thescrews 28.

Since each guide shaft is bent, adjoining ring rolls are required thatvibration of each ring roll be easy and that the adjoining ring rolls becoupled so as to ensure the transmission of torque. Cylindrical membersare suitable for coupling the ring rolls since such members aredifficult to be deformed with respect to a force in a torsionaldirection and relatively easy to be deformed with respect to in abending direction. From this viewpoint, it is preferable that adjoiningring rolls are coupled by the flexible cylindrical member 26 shown inFIG. 3 or the rigid cylindrical member 58 shown in FIG. 4.

The flexible cylindrical member 26 is required to have a thick wall inorder to ensure the transmission of torque between the ring rolls.However, there is a possibility that such a thick wall degrades of theoscillating property of ring rolls. The formation of the annularoutwardly projecting portion in a central portion of the cylindricalmember in the width direction can bend the cylindrical member easy evenif the cylindrical member has a thick wall. Since the annular outwardlyprojecting portion has deformation loads repeatedly applied thereto incomparison with other portions of the cylindrical member, it ispreferable that the wall of the annular outwardly projecting portion isthicker than that of the other portions.

Although the transmission of torque between the ring rolls is ensured bythe rigid cylindrical member 58 as a rigid member, there is apossibility that the oscillating property of the ring rolls may bedegraded if no measures is adopted. The cylindrical member can be benteasily by providing the cylindrical member with a bellows shape. Thenumber of folds of the bellows shape is determined to satisfy therequirements stated above, considering the material, the wall thicknessand so on of the cylindrical member.

As shown in FIG. 1, the conveyor rolls 12, 12 . . . according to thisembodiment are provided so that the distances between adjoining conveyorrolls are unequal. The present invention is constructed with severalconveyor rolls, for example at least three or at least four conveyorrolls, of the conveyor path being spaced apart by unequal distances. Thedistances means horizontal distances between central rotational shaftsof adjoining conveyor rolls as shown in FIG. 5. The unequal distancesshown in FIG. 1 will be explained in detail, referring to FIG. 5. Sevenconveyor rolls 12A-12G which are provided from the outlet 17 of theheating furnace 16 in that order are set so that distances (P1-P6)between the respective conveyor rolls are different. The distances areset so as to gradually expand toward the downstream side(P1<P2<P3<P4<P5<P6). In the shown example, P1 is equal to 60 mm, and P2,P3, P4, P5 and P6 gradually increase by 4 mm, respectively.

The distances (P1-P3) of the conveyor rolls 12A-12D which are located inthe vicinity of the outlet 17 of the heating furnace 16 are set so as tominimize the amount of sagging of She leading portion 19 of the glasssheet 18. The distances between the eighth and its subsequent conveyorrolls 12, 12 . . . are set to repeat the distances of P1-P6 or to beunequal one another. The unequality may include a case wherein alldistances are unequal and a case wherein some of the distances areunequal. A small number of unequal distances may result in insufficientcontribution to a decrease in the optical distortion. In order to copewith this problem, it is preferable that a certain number of distancesare unequal one another. In particular, it is preferable that thedistances are gradually changed as in the shown example since theprovision of the conveyor rolls can be effectively carried out and thegradual changes can remarkably contribute to a decrease in the opticaldistortion.

Now, the operation of the conveyor rolls 12 according to this embodimentwill be described, referring to FIG. 6. In FIG. 6 is shown atransitional view showing how the glass sheet 18 which has beendelivered from the outlet 17 of the heating furnace 16 is conveyed bythe plural conveyor rolls 12A-12E . . . . The glass sheet 18 is bentinto a certain shape, being conveyed on the conveyor rolls 12A-12E . . ..

As shown in FIG. 6(A), when the glass sheet 18 has the leading portion19 contacted with the conveyor roll 12A, the leading portion 19 iscooled by being removed heat by the conveyor roll 12A. As a result, theglass sheet 18 sags downwardly by heat shrinkage (B). As shown in (C),the sagged leading portion 19 runs onto the conveyor roll 12B whenpassing the conveyor roll 12B. This creates a state that the entireglass sheet 18 is slightly lifted. As shown in (D), when the leadingportion 19 has passed the conveyor roll 12B, the entire glass sheet 18returns to the position before being lifted, and the glass sheet 18contacts with the conveyor rolls 12A, 12B. (E) and (F) are viewesshowing a repeat of the operations in (C) and (D). As explained, theglass sheet 18 is conveyed on the conveyor rolls 12A-12E . . . , beingslightly vibrated in a vertical direction because of the presence ofsuch sagging motion of the leading portion 19.

Attention is directed to arbitrary points a, b, c, d and e on the glasssheet 18 (actually, lines perpendicular to the conveyance direction) in(B)-(F). The point a rises (C) after having contacted with the conveyorroll 12A (B). When the glass sheet 18 has lowered (D), the point a goesbeyond the conveyor roll 12B and is present between the conveyor roll12B and the conveyor roll 12C. When the glass sheet 18 lowers after thepoint b has been present above the conveyor roll 12A (C), the point bcontacts with the conveyor roll 12B (D). The point c is present betweenthe conveyor roll 12B and the conveyor roll 12C (E) after havingcontacted with the conveyor roll 12A (D). The point d which has notcontacted with the conveyor roll 12A or the conveyor roll 12B contactswith the conveyor roll 12C when the glass sheet occupies a positionshown in (E). On the other hand, the point e which has not contactedwith any one of the conveyor rolls 12A-12C contacts with the conveyorroll 12D when the glass sheet occupies a position shown in (F).

As explained, the mode according to the present invention allows anypositions on the glass sheet 18 to contact with at least one conveyorroll 12 since the distances between the conveyor rolls 12A-12E . . . areset so as to be unequal. As a result, the optical distortion that occursin the glass sheet 18 can be dispersed to prevent striped defects fromcausing in the glass sheet 18, providing the glass sheet 18 with goodquality.

According to this mode, the glass sheet 18 can be smoothly conveyedsince the amount of sagging of the leading portion 19 is minimized byadopting such arrangement wherein the distances (P1-P3) between theconveyor rolls 12A-12D in the vicinity of the outlet 17 of the heatingfurnace 16 are narrow. The distances between conveyor rolls in thevicinity of the outlet of the heating furnace may be converselyextended.

When a glass sheet which has been delivered from the outlet of theheating furnace contacts with conveyor rolls in the most upstream side,the conveyor rolls remove heat from the glass sheet to cool the glasssheet, causing the glass sheet to sag. If the distances between conveyorrolls in the vicinity of the outlet of the heating furnace are wide, theamount of sagging of the leading portion increases and the leadingportion enters spacing between the conveyor rolls, causing conveyancetrouble, in some cases. The amount of sagging of the leading portion canbe minimized by adopting such arrangement that the distances betweenconveyor rolls in the vicinity of the outlet of the heating furnace arenarrow. By such arrangement, a glass sheet can be smoothly conveyed toreduce the optical distortion due to conveyance trouble. From thisviewpoint, it is preferable that the distances between conveyor rollsprovided in the vicinity of the outlet of the heating furnace are set tobe narrower than the distances between the subsequent conveyor rolls.

The distances (P1-P6) of the conveyor rolls 12 may be adequately set,depending on the conveyance speed of the glass sheet 18 or the diameterof the conveyor rolls 12. Specific methods to consider the conveyorspeed and the diameter will be explained later on.

Glass sheets have been heated in the heating furnace 16 are normallytempered by quenching after the glass sheets have been bent on theconveyance path 14. If the temperature of the glass sheets lowers toomuch, the tempering treatment can not be carried out in sufficientfashion. It is necessary to make a drop in the temperature of the glasssheets on the conveyance path 14 as small as possible.

In principle, it is possible to prevent the glass sheets from beingcooled to a temperature lower than the temperature required for thetempering treatment by increasing the conveyance speed of the glasssheets. On the other hand, if the conveyance speed of the glass sheetsincreases too much, the glass sheets jar during conveyance, causingconveyance trouble. From this viewpoint, it is preferable that theconveyance speed of the glass sheets is in a range from 400 mm/sec to600 mm/sec. Under the circumferences, it is preferable that the entirelength of the conveyor path in the conveyance direction is in a rangefrom 1,300 mm to 2,000 mm, considering a drop in the temperature of theglass sheets during conveyance and a temperature capable of bending theglass sheets.

It is preferable that the conveyor path 14 has a width in a directionperpendicular to the conveyance direction in a range from 800 mm to1,200 mm. A width in such range can cope with variety of dimensions ofglass sheets when glass sheets for e.g. automobile side-lights are bent(normally the glass sheets are bent in a width direction perpendicularto the conveyance direction). Glass sheets for most automobileside-light have a width in a direction perpendicular to the conveyancedirection extending from around 300 mm to around 600 mm. The fact thatthe width of the conveyor path 14 in the direction perpendicular to theconveyance direction is in the range from 800 mm to 12,000 mm means thatthe conveyor rolls 12 per se have a length from around 800 mm to around12,000 mm (it is not considered that the conveyor rolls are bent). Inorder to provide a certain mount of rigidity to the conveyor rollshaving a length from around 800 to around 12,000 mm, it is preferablethat the conveyor rolls 12 have a diameter in a range from 40 mm to 100mm.

If the distances between the conveyor rolls are too great, glass sheetssag into spacing between the conveyor rolls during conveyance. From thisviewpoint, the upper limit of the distances are in a range from 80 mm to120 mm. When the distances are gradually increased toward the downstreamdirection as stated earlier, the distances are returned to the distancesin the vicinity of the outlet of the heating furnace at a location withthe maximum distance, and the subsequent distances are graduallyincreased toward the downstream direction again (such arrangement isrepeated when necessary).

Before glass sheets completely accommodate to bent profiles of theconveyor rolls 12, the glass sheets have lateral edges extending in theconveyance direction supported by the conveyor rolls 12 (there is a gapbetween a central region of the glass sheets and the conveyor rolls).Thus, the glass sheets have the central region sagged downwardly,providing a bent shape to the glass sheets.

In order to smoothly convey the glass sheets, it is required that theglass sheets have the supported portions thereof located at an almostconstant level in a vertical direction. When the glass sheets have thesupported portion maintained at such constant level, the bent conveyorrolls have end portions thereof positioned above and central portionthereof positioned under the glass sheets. Since the respective conveyorrolls have different curvatures, the respective conveyor rolls have theend portions positioned at different level. Since the curvatures of theconveyor rolls gradually increase toward the conveyance direction, thelevels of the end portions of the conveyor rolls gradually rise towardthe conveyance direction. From this viewpoint, it is preferable thatsprockets of the respective conveyor rolls are coupled by chains asmeasures to provide the respective conveyor rolls with rotationalmovement. Although the levels of the end portions of the conveyor rollsgradually increase toward the conveyance direction, the differencesbetween the levels can be absorbed by the chain to smoothly transmit therotary movement.

In order to modify the respective distances between the conveyor rollsin a case with the chain used as stated earlier, it is simple to removeelements of the chain. Such procedure can decrease the distances by alength corresponding to chain elements between adjoining conveyor rolls(¼ of the length of a chain element). Since the chain per se arerequired to have a certain degree of rigidity to provide the conveyorrolls with the rotational movement, the chain elements are also requiredto have a preferable size. From this viewpoint, it is preferable thatthe distances are modified by a shortest length in a range form 2 mm to10 mm. Consideration is directed to the entire length of the conveyorpath of 1,300 mm to 2,000 mm as well as the preferable diameter range ofthe conveyor rolls and the preferable upper limit of the distancesbetween the conveyor rolls. According this consideration, it ispreferable that the conveyor rolls are provided at different distancesthough distances having the same length are present at 2 to 10locations, in particular, 2 to 5 locations in the conveyor path. Whenthe distances are provided so that arrangements with gradually increaseddistances are repeated from the outlet of the heating furnace, it ispreferable that the repeated arrangements are provided at 2 to 10locations, in particular 2 to 5 locations.

As explained, in accordance with the bending method and the bendingapparatus for glass sheets of the present invention, at least some ofdistances between the plural conveyor rolls can be set so as to beunequal, forming glass sheets having good quality and free from opticaldistortion.

What is claimed is:
 1. A method for bending glass sheets comprising thesteps of: heating a glass sheet in a heating furnace a certain bendingtemperature; and bending the heated glass sheet on a conveyer pathincluding a plurality of conveyor rolls provided from an outlet of theheating furnace toward a downstream direction and having certaincurvatures, wherein the glass sheet is bent under the weight of theglass sheet as the glass sheet is conveyed along the conveyor path, andwherein at least three of the plurality of conveyor rolls within aforming section of the conveyor path are spaced apart by unequaldistances.
 2. A method for bending glass sheets according to claim 1,wherein the unequal distances are different from distances betweenadjoining conveyor rolls, whereby the glass sheet is bent with everycontact point between the glass sheet and the conveyor rolls duringconveyance being different.
 3. A method for bending glass sheetsaccording to claim 1 wherein the conveyor path has a length in aconveyance direction set in a range from 1400 mm to 2000 mm.
 4. A methodfor bending glass sheets according to claim 1, wherein conveyor rollshaving a diameter in a range from 40 mm to 100 mm are used as theplurality of conveyor rolls.
 5. A method for bending glass sheetsaccording to claim 1, wherein the plurality of conveyor rolls are spacedapart by a first shortest distance and a second shortest distance havinga difference in a range from 2 mm to 10 mm.
 6. A method for bendingglass sheets according to claim 1, wherein a distance between adjoiningconveyor rolls near to the outlet of the heating furnace is set so as tobe narrower than a distance between subsequent adjoining conveyor rolls.7. An apparatus for bending glass sheets comprising: a heating furnaceconfigured to heat glass sheets to a bending temperature; a conveyorconfigured to convey the glass sheets in the heating furnace; and aconveyer path including a plurality of conveyor rolls provided from anoutlet of the heating furnace toward a downstream direction and havingcertain curvatures, wherein the heated glass sheets are conveyed on theconveyor path to be bent in a desired shape, and wherein at least fourof the plurality of conveyor rolls of the conveyor path are spaced apartby unequal distances.
 8. An apparatus according to claim 7 wherein theconveyor path has a length in a conveying direction extending in a rangefrom 1400 mm to 2000 mm.
 9. An apparatus for bending glass sheetsaccording to claim 7, wherein conveyor rolls having a diameter in arange from 40 mm to 100 mm are used as the plurality of conveyor rolls.10. An apparatus for bending glass sheets according to claim 7, whereina first shortest distance and the second shortest distance among thedistances between the plurality of conveyor rolls has difference in arange from 2 mm to 10 mm.
 11. An apparatus for bending glass sheetsaccording to claim 7, wherein a distance between adjoining conveyorrolls near to the outlet of the heating furnace is set so as to benarrower than a distance between subsequent adjoining conveyor rolls.12. An apparatus for bending glass sheets according to claim 11, whereinthe plurality of conveyor rolls are provided such that distances betweenadjoining conveyor rolls are gradually increased toward a downstreamdirection in a conveyance direction, and the distances have a maximumvalue in a range from 80 mm to 120 mm, and that the plurality ofconveyor rolls are provided such that the distances are returned to avalue of the distance between the conveyor rolls near to the outlet ofthe heating furnace at a position where the distances are graduallyincreased to become the maximum value, and the distances are graduallyincreased toward the downstream direction in the conveyance directionagain.